This invention relates to the cementing of casing in oil and gas wells by the use of cementing plugs. More specifically, this invention relates to a new and improved plug launching system and surface injection manifold. The cementing plug injection system is designed to selectively release one or more plugs into the well casing ahead of or behind a cement slurry to reduce contamination of the cement. A first cementing plug may optionally be used ahead of an optional chemical spacer fluid, which can further insure a minimum amount of chemical interference with a cement slurry and a minimal amount of contamination. This optional first plug and spacer fluid would then be followed by a second plug which wipes the drilling fluid from the walls of the casing ahead of the cement slurry, which second cementing plug is then followed by a cementing top plug on command. The top plug follows the cement and further prevents contamination or channeling of the cement with the drilling fluid or fluid used to displace the cement.
The new and improved apparatus of the present invention selectively injects at desired intervals at one or more cementing plugs from an assembly which provides a mandrel and may utilize a slip joint which may be suspended inside the casing at any desired location or depth, which mandrel is fitted with one or more cementing plugs which are releasably retained upon the mandrel by shear rings of different capacities, or are held in position above a restriction sleeve. An injection manifold up stream of the mandrel and plug assembly, which can be skid mounted, is provided with an assembly of injection cylinders fitted with spring loaded pistons, which can be loaded or dressed with pick-up balls, which in turn each are held in a loaded position by a second set of air cylinders each fitted with a spring loaded piston, which in the loaded position extends to retain a pick-up ball within the first cylinder set. One ball launcher and pick-up ball is sized and used for each cement plug mounted to the mandrel. Each cement plug is provided with an interior passage, and at or near the lower most end of each cement plug is a landing ring sized for a pick-up ball of a particular diameter. Pick-up balls for the lower cement plugs are slightly smaller in diameter than pick-up balls for upper cement plugs. The plugs are launched by sequentially injecting the pick-up balls, the smaller ones first, into the stream of cement of slurry, or into the drilling fluid stream. The pick-up ball is carried to its landing in a particular cement plug and pressure build up shears a shear ring holding that cement plug to the mandrel combination assembly (or optionally forces one plug past a restriction sleeve), and the cement plug is thereby launched for the purposes as described above. The method and apparatus of the present invention is further provided with both a fail-safe positive mechanical indication for the launching of each pick-up ball, and with a further magnetic pick-up indication of launching for each of the pick-up balls, to provide positive indication when a plug or plugs have been launched. The method and apparatus of the present invention provides a highly adaptable, efficient and inexpensive means of injecting one or more cementing plugs which can be used on any diameter casing, and further can be used for both surface plug launching or subsea plug launching.
The use of cementing plugs in oil and gas well cementing operations has long been known. The prior art operation is best described in U.S. Pat. No. 4,427,065 to James S. Watson. Watson discloses a cylindrical cementing plug container assembly which is loaded with one or more cementing plugs stacked vertically one above the other. This entire cementing plug container housing is mounted above the casing. Each plug is held within its housing by a mechanical cam lock holding/release device. The cam lock release devices are separately remotely actuateable, and when actuated each device will move the plug holder out of the plugs path where upon each plug is pulled/pushed by a combination of fluid flow, vortex action and gravity into the vortex fluid stream where it is caught by the moving fluid and pumped downhole. The cumbersome Watson cementing plug container, which in the usual practice contains two cementing plugs, projects a significant distance above the casing, and thereby necessitates much longer elevator bails than would be required without the cementing plug container assembly. Furthermore, if it is desired to provide more than two cementing plugs, either a separate plug container in a longer length projecting even further above the casing must be fabricated, or some means of connecting a series of the cementing plug containers which utilize twin displacement cementing plugs must be fashioned. If this is not done, Watson provides no significant safety over the earlier method (also described in U.S. Pat. No. 4,427,065) of removing and replacing the dome each time a plug is inserted with the consequent expenditure of time, expense, and creation of hazardous working conditions. In addition, each of the various casing sizes requires a different Watson cementing plug container housing assembly.
The new and improved method and apparatus for injecting displacement cementing plugs disclosed in the present invention remedies all of the short fallings of the prior art devices, and provides method and apparatus for injecting one or more displacement plugs which is readily adaptable to all casing sizes, which can be used either sub-sea or at surface locations, and which provides a simple and efficient skid mounted injection header assembly which provides positive physical evidence directly related to the launching of each displacement plug in the series. Also disclosed in the primary embodiment are a new and improved cement shoe and plug collar which each alone are significant improvements over prior art devices.